Ascochyta Blight of Chickpeas

Note Number: AG1186
Published: June 2005
Updated: August 2008

Ascochyta blight of chickpeas is caused by the fungal pathogen Ascochyta rabiei. In 1998 there was a serious outbreak of the disease in Victoria, South Australia and NSW, which destroyed many crops. A number of varieties with improved resistance to ascochyta blight are now available. Variety selection and understanding the associated disease management package is critical for success.

Symptoms

This disease is usually first noticed in late winter when small patches of blighted plants appear throughout the paddock.
The disease spreads during cool, wet weather from infected plants to surrounding plants by rain splash of spores. This creates large blighted patches within crops (see Figure 1).

Initially ascochyta blight appears on the younger leaves as small water-soaked pale spots. These spots rapidly enlarge under cool and wet conditions, joining with other spots on the leaves and blighting the leaves and buds (see Figure 2). Small black spots (pycnidia), less than 1 mm in diameter, can be seen in the affected areas. In severe cases of infection the entire plant dries up suddenly.

Elongated lesions can often form and girdle the stem. The stem may die and break off. Regrowth may occur from the broken stem. Affected areas on the pods tend to be round, sunken, with pale centres and dark margins (see Figure 3).

The fungus can penetrate the pod and infect the seed. Severe pod infection usually results in reduced seed set and infected seed. When infected seeds are sown, the emerging seedlings will develop dark brown lesions at the base of the stem. Affected seedlings may collapse and die (damping-off).

Economic importance

The widespread occurrence of this disease in 1998 had a negative impact on the chickpea growing industry. To successfully grow varieties with susceptible to moderately resistant ascochyta blight ratings, foliar fungicides need to be applied throughout the growing season or serious yield losses may occur. Varieties rated as resistant (such as Genesis™090 and Genesis™509) still require at least one fungicide at early podset, but the risk of yield loss is minimal.

When selecting varieties the added cost of fungicide applications needs to be considered before selecting and growing susceptible to moderately resistant varieties.

Disease cycle

This fungal disease has an asexual (non-sexual) and sexual stage; the asexual stage is most common in Australia. In this stage the fungus survives mainly on infected seed and on crop residues.

Spores of the fungus produced on crop residues can be carried onto new crops by wind. Infection can occur at any stage of plant growth, provided conditions are favourable. Moisture is essential for infection to occur.

During wet weather, the disease can spread further than in dry conditions because spores of the fungus are carried onto neighbouring plants by wind and rain splash.

Management

Management requires a combination of farm hygiene, resistant varieties, crop monitoring and the use of fungicides. When growing a new variety, obtain a copy of the variety management package for information on specific disease management.

• A key strategy is to consider growing a resistant variety such as Genesis™509 or Genesis™090. Note, a fungicide application is still required at early podding to protect seed quality.

For chickpea varieties (rated susceptible to moderately resistant) the following management strategies should be applied.

• Use seed from a paddock where ascochyta was not detected or was well managed.
• Treat all seed with a seed dressing registered for ascochyta blight control.
• Choose a paddock at least 500 metres from last years chickpea crop.
• Generally the first fungicide spray will need to be applied 4-6 weeks after sowing. Moderately resistant varieties such as Almaz will require 2 – 4 strategic sprays throughout the growing season. The moderately susceptible varieties, such as Howzat, will require spraying every 2-3 weeks. Very susceptible varieties such as Kaniva will require spraying at least fortnightly throughout the growing season.
• Note, sprays only protect the plant parts contacted by the spray, subsequent plant growth will not be protected.
• A fungicide spray at pod set is essential to ensure production of premium quality seed.
• Always disinfect machinery, vehicles and boots once they have been in an infected crop.

Breeding programs in Australia are developing improved ascochyta blight resistant lines of chickpeas. All current resistant varieties and future releases will still require spraying at podding time, as their pods are susceptible to infection. However, the greatly reduced number of spray applications required for resistant varieties make chickpeas a valid crop option and profitable to grow.

As resistant varieties become grown over larger areas there is likely to be a reduction in the amount of ascochyta blight inoculum present. This should reduce the risk of further serious disease outbreaks.

Further References

More information on chickpeas and their diseases can be found at www.dpi.vic.gov.au/notes (click on Crops and Pastures, then select Legume Crops)

www.pulseaus.com.au Wayne Hawthorne and others

The Victorian Winter Crop Summary2008, available at www.dpi.vic.gov.au (click on Crops and Pastures, then Grain Crops)

National Variety Trials Online, www.nvtonline.com.au

Acknowledgements

This Information Note was originally written by Trevor Bretag,,Wendy Bedggood and Kristy Hobson, Horsham in June 2005.

This updated version was developed by Helen Richardson and Kristy Hobson, Horsham.